For several years, automated “sort machines” have been available which sort large volumes of documents (e.g. letters, postcards, checks, flats, and the like) into groups having a common identifying criteria (e.g. Zip Codes, mail boxes, etc.). A sort machine is typically comprised a “front end” or feeder section and one or more “stacker sections”. The front end feeds the pieces, one-by-one, past a reader (e.g. optical character reader (“OCR”), bar code reader (“BCR”), or the like) and onto a transport that carries it to a designated sort pocket in the stacker section(s).
As the piece passes the reader, the desired criteria on a piece is read and a signal is generated that, in turn, is processed to generate a designation signal for that particular piece. This designation signal, in turn, triggers a diverter or “gate” at the designated pocket in the stacker section as the piece approaches to divert the piece from the transport into the designated pocket where it is stacked with other pieces having the same identifying criteria. Such machines are well known and are commercially-available, e.g. Vsort™ Flat Sort Machine, NP8000™ Sort Machine, both manufactured and distributed by National Presort, Inc., Dallas, Tex.
Many present sort machines are comprised of a plurality of vertically stacked tiers of sort pockets which increase the number of pockets without substantially increasing the machine's “foot print” (floor area required for the machine). In machines of this type, the letters are read and directed by a Level Distribution Unit or elevator system to a particular tier on which its respective sort pocket is located. For example, if a sort machine has four tiers, only approximately 25% of the letters being fed will go to each of the tiers. This means that approximately 75% of the sort capacity of each tier goes unutilized. It can be seen that if the unused capacity on each tier can be reduced, the throughput of the machine can be significantly increased.